This invention relates to a graft polymer obtained by subjecting a cyclic ester to ring-opening polymerization in the presence of a cellulose derivative and to a process for preparing the graft polymer.
A large number of methods have been proposed in the past to make a cellulose derivative more easily processable by graft-polymerizing an unsaturated monomer such as a vinyl compound to the cellulose derivative. For example, Japanese Patent Laid-Open No. 48032/1975 discloses a process for preparing a graft copolymer by copolymerizing cellulose acetate butyrate or nitrocellulose having at least one of a copolymerizable unsaturated group and a functional group consisting of a carbon-to-hydrogen bond whose hydrogen can be withdrawn by a radical, with a polymerizable monomer. "Kobunshi Jikkengaku Dai 6 kan, Kobunshi-hanno (Polymer Experiment, Vol. 6, Polymer Reaction)", edited by Polymer Experiment Editing Committee of Polymer Society (published by Kyoritsu Shuppan, 1978), p.p. 147-192, describes a graft block reaction to a cellulose derivative together with an ordinary graft block reaction.
However, the products obtained by these reactions are primarily reaction products of addition polymerization such as radical or ionic polymerization of a polymerizable monomer and the yield of graft polymer or block copolymer with the cellulose derivative is generally extremely low.
Graft polymerization of cellulose itself has also been attempted variously and is disclosed in "Polymer Experiment, Vol. 6, Polymer Reaction", p.p. 147-192 described above or in "Koza Jugo Hanno-ron (10), Koubunshi no Kagaku Honno (1) (Lecture, On Polymer Reaction (10), Chemical Reaction of Polymer (1))" by Shin Okawara (by Kagaku Dojin, 1972), p.p. 56-74. In the graft polymerization to the cellulose itself disclosed in these references, too, the polymerizable monomer is primarily a compound that can be polymerized by addition polymerization (radical polymerization, ionic polymerization, etc) in the same way as in the case of the cellulose derivative. Only a few reports are known in which ethylene oxide, ethyleneimine or .beta.-propiolactone is reacted with cellulose itself.
The inventors of the present invention have carried out intensive studies in order to obtain cellulose derivatives that are not known heretofore from the literature but are industrially useful and have high solubility unlike the grafted or blocked products of the cellulose derivative described above. As a result, the inventors have succeeded in producing on an industrial basis entirely novel graft polymers by subjecting a cyclic ester to ring-opening polymerization in the presence of a cellulose derivative, and have found also that the resulting graft polymer is a novel polymer material having transparency, good film formability and good solubility. Thus, the present invention is completed.